1. Field of the Invention
This invention relates to an image stabilizing photographing apparatus, and particularly to an image stabilizing photographing apparatus suitable for the image pickup optical system of a video camera, an electronic still camera or the like in which the movement of an image on the surface of an image pickup element (when the image pickup apparatus is inclined by vibration or the like) is corrected to thereby prevent blurred images.
2. Related Background Art
There have heretofore been proposed various image stabilizing apparatuses in which the movement of an image on the surface of an image pickup element caused by the vibration, inclination or the like of the image pickup apparatus is corrected so that a still image may be obtained.
For example, U.S. Pat. No. 3,212,420 proposes an image stabilizing apparatus in which, as shown in FIG. 2 of the accompanying drawings, a refraction type variable apex angle prism P is mounted forwardly of an image pickup optical system S and the apex angle of the variable apex angle prism P is varied correspond to the vibration of the image pickup apparatus to thereby deflect an image on an image pickup surface and correct the movement of the image.
In the method as shown in FIG. 2 wherein correction means by the variable apex angle prism is disposed forward of the image pickup optical system to thereby correct the movement of the image caused by the vibration of the image pickup apparatus, the presence of the color dispersion effect in the material of the variable apex angle prism would cause a chromatic difference of magnification proportional to the focal length f of the image pickup optical system S and the degree of dispersion of the variable apex angle prism P, thus deteriorating the imaging performance.
For example, when a light of any reference wavelength .lambda..sub.o deflected by the variable apex angle prism P passes through the variable apex angle prism P and thereafter enters the image pickup optical system S in parallel to the optic axis of the image pickup optical system S, a light of a different wavelength .lambda..sub.n (n=1, 2, 3, . . . ) enters the image pickup optical system S in the subsequent stage at an emergence angle of inclination .tau..sub.n (an included angle between the optic axis and the direction of incidence) (n=1, 2, 3, . . . ) corresponding to the degree of dispersion of the material of the variable apex angle prism P. The chromatic difference of magnification .DELTA.y.sub.n (n=1, 2, 3, . . . ) of the light of each wavelength .lambda..sub.n caused at this time by the influence of the variable apex angle prism P can be expressed by the following equation (1): EQU .DELTA.y.sub.n =f.multidot.tan.tau..sub.n EQU (n=1, 2, 3, . . . ) (1)
Assuming at this time that, for example, as conditions for manual photographing by the use of a hand-held video camera, the angle of inclination .theta. of the deflected image corresponding to the shake of the apparatus with respect to the optic axis of the image pickup optical system S (hereinafter referred to as the compensation deflection angle) is 3.degree., the focal length f of the image pickup optical system S is 50 mm and use is made of silicone rubber in which the refractive indices of the refraction type variable apex angle prism P for R light (red: .lambda..sub.R .congruent.610 nm), G light (green: .lambda..sub.G .congruent.530 nm) and B light (blue: .lambda..sub.B .congruent.460 nm) are n.sub.R =1.4052, n.sub.G =1.4097 and n.sub.B =1.4141, respectively, the chromatic difference of magnification .DELTA.y.sub.n between channels obtained from the above-mentioned equation (1) is .DELTA.y.sub.B =-28 .mu.m and .DELTA.y.sub.R =18 .mu.m with G light as the reference.
Generally, to maintain ordinary imaging performance, it is considered to be desirable that the width of the chromatic difference of magnification between channels be less than 5-10 .mu.m.
Accordingly, the conventional method has suffered from the problem that, as described above, the chromatic difference of magnification is great and the imaging performance is deteriorated.
In contrast, Japanese Laid-Open Patent Application No. 61-223819 proposes an image stabilizing optical system having refraction type image deflecting means disposed forwardly of a photo-taking lens, and chromatic aberration correcting means for correcting aberration created by said refraction type image deflecting means.
However, this system has required an actuator such as a motor for driving said chromatic aberration correcting means eccentrically relative to the optic axis, which has led to the tendency that the entire apparatus including the optical system becomes bulky.
Also, the conventional variable apex angle prism has been formed of a visco-elastic material such as silicone rubber or liquid and therefore has encountered a great difficulty in following vibration of a high frequency (e.g. ten and several Hz or higher). This has led to the problem that good correction cannot be accomplished for image blur based on a minute vibration of high frequency components, for example, in the photographing from an automobile, a helicopter or the like.
On the other hand, U.S. Pat. No. 4,623,930 discloses a technique using an electrical means to stabilize an image formed on the image pickup surface of a CCD or the like against unexpected vibration.